/**
 * 链表-两两交换位置-力扣24
 */

public class Practice_33 {
    public static void main(String[] args) {
        ListNode head = new ListNode();
        head.val = 2;

        ListNode second = new ListNode();
        second.val = 3;
        head.next = second;


        ListNode third = new ListNode();
        third.val = 4;
        head.next.next = third;

        ListNode four = new ListNode();
        four.val = 5;
        head.next.next.next = four;

        ListNode five = new ListNode();
        five.val = 6;
        head.next.next.next.next = five;

        ListNode six = new ListNode();
        six.val = 7;
        head.next.next.next.next.next = six;

        ListNode list = swapPairs(head);

    }

    public  static ListNode swapPairs(ListNode head) {
        ListNode imghead = new ListNode();//虚拟头节点
        imghead.next = head;//连接虚拟头节点和后续节点

        ListNode cur=imghead;
        while(cur.next!=null&&cur.next.next!=null){//注意先写cur.next 再写cur.next.next避免空指针异常
            ListNode tmp=cur.next;
            ListNode tmp1=cur.next.next.next;//交换位置后的2个节点之后的节点先存起来
            cur.next=cur.next.next;//实现交换位子
            cur.next.next=tmp;//实现交换位子
            cur.next.next.next=tmp1;//交换位置后和下一个节点连起来

            cur=cur.next.next;//cur走2步。走到要交换位子的前一个节点
        }

        return imghead.next;
    }

    static class ListNode {
        private int val;
        private ListNode next;
    }
}
